Body Weight, Body Composition, and Sport Chapter 14
Learning Objectives • Differentiate among body build, body size, and body composition • Find out what tissues of the body constitute fat-free mass • Discover how densitometry and several field techniques are used to assess body composition • Examine the relationship of relative leanness and fatness to performance in sport
Learning Objectives • Find out what guidelines best determine an athlete's goal weight • Learn why athletes should avoid crash dieting or fixating on a weight that is too low • Find out how much weight an overweight athlete can lose per week to maximize fat loss and minimize fat-free mass loss
Body Build, Size, and Composition • Body build- form or structure of the body • Muscularity (mesomorphy) • Linearity (ectomorphy) • Fatness (endomorphy) • Body size- determined by height and weight • Body composition- refers to the proportional make-up of the body
Models of Body Composition 60% 45% 20%
Fat-Free Mass vs. Lean Body Mass • Fat-free mass- composed of all the body’s nonfat tissue, including bone, muscle, organs, and connective tissue • Lean body mass- includes all fat-free mass along with essential fat • Difficult to measure so the fat mass/fat-free mass model is most often used
Body Composition • Better indicator of fitness than body size and weight • Being over-fat (not necessarily over weight) has a negative impact on athletic performance.
Body Composition • Standard height-weight tables do not provide accurate estimates of what an athlete should weigh, because they do not take into account the composition of the weight. • An athlete can be overweight according to these tables yet have very little body fat.
Assessing Body Composition • Densitometry (hydrostatic weighing) • Dual-energy X-ray absorptiometry (DEXA) • Air plethysomography • Skinfold fat thickness • Bioelectric impedance
Densitometry • Involves measuring the density of the athlete’s body • Dbody = Mbody/Vbody • Body mass: measured on a regular scale • Body volume: measured using hydrostatic (underwater) weighing accounting for water density and air trapped in lungs • Archimedes’ principle: a body immersed in water is buoyed up with a force equal to the weight of the water displaced
Densitometry • % body fat = (495/Dbody) – 450 • Density of water = 1.00 g/ml • Muscle = 1.10 g/ml • Fat = 0.901 g/ml • Inaccuracies in densitometry are due to variation in the density of the fat-free mass from one individual to another. • Age, sex, and race effect density of fat-free mass.
Dual-Energy X-Ray Absorptiometry (DEXA) Used to estimate bone density and bone mineral content as well as total body composition (fat mass and fat-free mass)
Air Plethysmography Uses air displacement technique to estimate total body volume
Body Composition and Performance • Maximizing fat-free mass • Desirable for strength, power, and muscular endurance • Undesirable for endurance or jumping sports if result is weight gain • Minimizing body fat • Desirable, especially in sport in which the body weight is moved through space • Improves speed, endurance, balance, agility, and jumping ability
Subject’s level of fatness (% body fat) Performance test Low Moderate High (<10%) (10-15%) (>15%) 75-yd dash (s) 9.8 10.1 10.7 220-yd dash (s) 29.3 31.6 35.0 Standing long jumpa (ft) 23.8 22.7 20.2 Sit-ups in 2 min 43.4 41.6 36.2 Note. The men in this study were classified into three levels of fatness: low, moderate, and high. aSum of three trials. The Effect of Relative Body Fat on Selected Performance Tests in Young Men
Risks with Severe Weight Loss • Dehydration • Chronic fatigue • Disordered eating and eating disorders • Menstrual dysfunction • Bone mineral disorders Female Athlete Triad
Appropriate Weight Guidelines • Maximize performance within the specific sport • Based on body composition • Emphasize relative body fat rather than total body mass • Use a range of relative fat values that are considered acceptable for the athlete’s age, sex, and sport/event
Parameter Measure Weight 72.6 kg (160 lb) Relative fat 25% Fat weight 18.2 kg (40 lb) (weight 25%) Fat-free weight 54.4 kg (120 lb) (weight – fat weight) Relative fat goal 18% (= 82% fat-free) Weight goal 66.3 kg (146 lb) (fat-free weight ÷ 82%) Weight loss goal 6.3 kg (14 lb) Computing a Weight Goal for Performance for a Female Swimmer
Weight Loss • When following very low calorie diets, much of the weight loss is from water, not fat. • Most severe diets limit CHO intake, which depletes CHO stores • Water is loss with CHO, which increases dehydration • Increased reliance on free fatty acids can lead to ketosis, which further increases water loss
Weight Loss • The combination of diet and exercise is preferred approach to optimal weight loss • Athletes should lose no more than ~0.5 to 1.0 kg (1.1-2.2 lb) per week until reaching upper end of desired weight range. • More rapid weight loss results in loss of fat-free mass
Edna Vicki Susan Body tissue DT % DP DT % DP DT % DP Muscle 1.065 46 0.490 1.065 41 0.437 1.065 46 0.490 Bone 1.350 17 0.229 1.350 22 0.297 1.260 17 0.214 Remainder 1.030 37 0.381 1.030 37 0.381 1.030 37 0.381 DFFM 1.100 1.115 1.085 Note. DT = density of the tissue; % = percent contribution of this tissue to the total-fat-free mass; DP = proportional density of the tissue (DT · %); DFFM = density of the fat-free mass, which is the sum of the proportional densities. Differences in the Density of Fat-Free Mass (DFFM) in Three Female Athletes